Prior art reflection type screen comprising a screen substrate or matrix which is made of a sheet of woven glass fibers or synthetic fibers, such a woven sheet which is impregnated with a resin such as vinyl chloride, a synthetic resin sheet of vinyl chloride, or a metallic sheet of aluminum; and a reflection layer which is deposited on the surface of the screen substrate made of these materials has been known.
The above-mentioned reflection layer is formed by applying a pearl paint or pearl ink in which titanium dioxide coated powders or mica flake fragments are dispersed in a binder made of a light transmitting resin or silver paint or ink containing powders of a metal such as aluminum on the surface of the screen substrate. Further, reflection type screen on which a multiplicity of transparent micro beads are arrayed to provide regression has been known.
A screen comprising a diffusion layer in which finely divided particles of crystal of calcite which acts as a light diffusing substance having a low light absorption are dispersed in a binder, said layer being laminated on the above-mentioned reflection layer has also been known.
If the diffusion on the screen is excessively increased on the reflection type screen, external disturbing light can not be distinguished from the projected light in a light room, leading to lowering of the contrast. Accordingly, the degree of the diffusion on the imaging face should be suppressed to some extent.
Since a large difference in a horizontal direction between the incident angle of the light to the screen at the peripheral area and the central area on a large size screen to be viewed having an aspect ratio of 16:9 which is becoming predominant will occur, a horizontal diffusion is necessary so that a view angle which is enough to cover the difference in angle can be obtained. The gain in a direction toward the front face of the screen can be increased by decreasing the diffusion degree of the screen. At this time viewing characteristics such as view angle and screen CCR (central/peripheral brightness ratio) would be deteriorated.
In view of the foregoing, the diffusion degree should be suppressed to some degree to enhance the contrast in a light room in the refection type screen. Reflection characteristics which cause the light diffusion to increase the view angle in a horizontal direction are required.
Prior art reflection type screen having a structure that is shown in FIG. 60 is disclosed in patent specification (Japanese laid-open patent publication No. 11-38509). This refection type screen 110 comprises a light diffusion layer 118 which is formed on the surface 116A of a substrate 116 of a prism sheet for diffusing projected images and a plurality of prisms 120 made of an optically transparent material which are in the form of stripe are extended and arrayed in a vertical direction of the screen on the reverse side 116B of the substrate 116. Each prism 120 has a section which is in the form of an equilateral triangle so that it has a given apex angle and a given side length. A light absorbing sheet 114 is disposed on and in parallel with the prism sheet 112 so that it faces a prism group on the rear side of the prism sheet 112. The light absorbing sheet 114 is black colored to substantially absorb the transmitted light on the side opposite to the rear side.
Eternal disturbing light R which is often incident on the screen surface at a high incident angle is absorbed by the light absorbing sheet 114 by being transmitted through the prisms in the reflection type screen of the patent specification 1.
FIGS. 61 through 63 are views explaining the function of the prism on the reflection type screen of the cited patent specification 1 and schematically show only the prisms 120 and the substrate 116 which constitute the reflection type screen. Reflection on the interface between portions of the prism 120 having different refractory indices will be considered in the reflection screen of the cited patent specification 1. Since the incident angle of the light projected on the reflection type screen 110 is in the range of 0° to 15° in a horizontal angle, the light which is incident to the reflection type screen 110 in a perpendicular direction is regressively reflected as shown in FIG. 61. In contrast to this, the light which is incident to the reflection type screen 110 at some incident angle will pass through a first prism interface shown in FIG. 62, or a second interface shown in FIG. 63 without being reflected thereon and will be absorbed by a light absorbing sheet 114. Due to such an action, a large different between the brightness of the light on the reflection type screen 110 at the central area and peripheral area thereof is caused, so that a problem that the view angle at the peripheral area and CCR (screen/peripheral area brightness ratio) deteriorates is invited. Such a deterioration of CCR becomes more remarkable if the screen is a wide screen.
As mentioned above, the reflection type screen 110 of the cited patent specification 1 aims at increasing the view angle by the operation of the prisms 120 which extend in a vertical direction and an improvement in the contrast of the projected light at a light place by absorbing the light having a high incident angle to the reflection type screen 110. However only light which is incident to the screen in a horizontal direction as is the case sun light is incident indoor at light place is considered. The contrast is improved by absorbing the external disturbing light which is incident in a horizontal direction with the light absorbing sheet 114 as mentioned above. However, no case in which external disturbing light is mainly incident to the reflection type screen 110 from an upper position as is an electric bulb is considered. In other words, when the prisms 120 extending in a vertical direction are used, an effect for absorbing the external disturbing light incident from an upper position can not be expected.
In other words, if the screen of the cited patent specification 1 is used indoors below an electric illumination bulb, a larger amount of the projected light which is incident on the peripheral area of the screen in a downward direction will pass through the prisms 120 as shown in FIGS. 62 and 63 and is ultimately absorbed. Accordingly, the projected light will not be returned to the viewers, so that the screen looks darker. The darkness becomes more remarkable in view of incident angle particularly on the wide screen.
Therefore, in view of the foregoing, characteristics such as excellent contrast in a light room, excellent view angle in a horizontal direction and excellent CCR of the screen are demanded for the reflection type screen.
The present invention was made in view of the above-mentioned circumstances. It is an object of the present invention to provide a reflection type screen having a high contrast even in a light room and a reflection type screen having an excellent horizontal view and an excellent screen CCR in addition to the high contrast.
Cited Patent Specification 1:
Japanese Laid-Open Patent Publication No. 11-38509